深入HTTP

@WebFilter(filterName = "imgFilter",value = "/img/*")
public class MckzFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("过滤器开始");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("梅川酷子");
        //获取上一个请求地址
        HttpServletRequest httprequest=(HttpServletRequest)request;
        HttpServletResponse httpresponse=(HttpServletResponse)response;
        //获取上一个请求地址
        String referer = httprequest.getHeader("Referer");
        //获取本项目的请求地址
        String serverName = httprequest.getServerName();
        System.out.println(referer+"\t"+serverName);
        //判断
        //如果上一个请求地址为空或者非本项目的请求地址拦截
        if(referer==null||!referer.contains(serverName)){
            request.getRequestDispatcher("/img/asd.jpg").forward(request,response);
            return;
        }
        chain.doFilter(request,response);

    }

    @Override
    public void destroy() {
        System.out.println("过滤器关闭");
    }
}